1. Field of the Invention
The present invention relates to a technique by which a crystalline silicon film having a monocrystal-like region or a substantially monocrystal-like region is formed on a substrate having an insulating surface made of glass or the like. Also, the present invention relates to a technique by which a thin-film semiconductor device represented by a thin-film transistor is formed by using the crystalline silicon film.
2. Description of the Related Art
In the recent years, attention has been directed to a technique by which a thin-film transistor is constituted by using a thin-film silicon semiconductor film (a thickness of about several hundred to several thousand xc3x85) which is formed on a substrate having a glass substrate or an insulating surface. What the thin-film transistor is applied to with the most expectancy is an active matrix type liquid-crystal display unit.
The active matrix type liquid-crystal display unit is structured such that liquid crystal is interposed between a pair of glass substrates and held therebetween. Also, it is structured such that a thin-film transistor is disposed on each of pixel electrodes which are arranged in the form of a matrix of several hundred x several hundred. Such structures require a technique by which the thin-film transistor is formed on a class substrate.
In the formation of the thin-film transistor on the glass substrate. it is necessary to form a thin-film semiconductor constituting thethin-film transistor on the glass substrate. For the thin-film semiconductor formed on the glass substrate, an amorphous silicon film formed through the plasma CVD technique or the low pressure thermal CVD technique is generally utilized.
Under existing circumstances, the thin-film transistor using the amorphous silicon film is practically used. However, in order to obtain display with a higher image quality, there is demanded a thin-film transistor utilizing a silicon semiconductor thin film (called xe2x80x9ca crystalline silicon filmxe2x80x9d) with a crystalline property.
Techniques disclosed in Japanese Patent Unexamined Publication No. 6-232059 and Japanese Patent Unexamined Publication No. 6-244103 made by the present applicant have been well known as a method of forming the crystalline silicon film on the glass substrate. The techniques disclosed in those publications are that a crystalline silicon film is formed on a glass substrate through a heat treatment under a heating condition which can be withstood by the class substrate, that is, approximately at 550xc2x0 C. for 4 hours, by utilizing a metal element that promotes the crystallization of silicon.
However, the crystalline silicon film obtained by the method using the above-mentioned techniques is not available to a thin-film transistor that constitutes a variety of arithmetic operating circuits. memory circuits or the like. This is because its crystalline property is insufficient and a characteristic as required is not obtained.
As the peripheral circuits of the active matrix type liquid-crystal display unit or the passive type liquid-crystal display unit, there are required a drive circuit for driving a thin-film transistor disposed in a pixel region, a circuit for dealing with or controlling a video signal, a memory circuit for storing a variety of information etc.
Of those circuits, the circuit for dealing with or controlling a signal and the memory circuit for storing a variety of information are required to provide a performance equal to that of an integrated circuit using a known monocrystal wafer. Hence, when those circuits are to be integrated using the thin-film semiconductor formed on the glass substrate, the crystalline silicon film having the crystalline property equal to that of monocrystal must be formed on the class substrate
As a method of enhancing the crystalline property of the crystalline silicon film, there have been proposed that the obtained crystalline silicon film is subjected to a re-heating treatment or to the irradiation of a laser beam. However, it has been proved that, even though the heat treatment or the irradiation of a laser beam is repeatedly conducted, it is difficult to dramatically improve the crystalline property.
Also, a technique in which a monocrystal silicon thin film is obtained by using the SOI technique has now been researched. However, since the monocrystal silicon substrate cannot be utilized for the liquid-crystal display unit, the above technique cannot be applied directly to the liquid-crystal display unit. In particular, in the case of using a monocrystal wafer, it is difficult to apply the SOI technique to the liquid-crystal display unit having a large area a demand of which is expected to increase in the future because of a limited substrate area.
The present invention has been made in view of the above problems, and theretore an object of the present invention is to provide a technique in which a monocrystal or monocrystal-like region is formed on a substrate having an insulating surface, in particular, on a glass substrate, and a thin-film semiconductor device represented by a thin-film transistor is formed by using that region.
In order to solve the above-mentioned problems, according to one aspect of the present invention, there is provided a method of manufacturing a semiconductor, comprising the steps of:
forming a first semiconductor film on a substrate having an insulating surface;
applying an energy to said first semiconductor film to crystallize said first semiconductor film;
patterning said first semiconductor film to form a region that forms a seed crystal;
etching said seed crystal to selectively leave a predetermined crystal surface in said seed crystal;
covering said seed crystal to form a second semiconductor film; and
applying an energy to said second semiconductor film to conduct a crystal growth from said seed crystal in said second semiconductor film.
In the above-mentioned structure, a silicon film is typically used for the first and second semiconductor films. Also, in general, an amorphous silicon film formed through the CVD technique is used for the silicon film.
The reason why the predetermined crystal surface is selectively left is to conduct the crystal growth so as to produce crystal more approximating monocrystal. Leaving the predetermined crystal surface may be achieved by using etching means having a selectivity with respect to the predetermined crystal surface. For example, using an etchant resulting from mixing H2O of 63.3 wt %. KOH of 23.4 wt % and isopropanol of 13.3 wt % together, a (100) tace can be selectively left, as a result of which the seed crystal covered with the (100) face can be selectively left.
Also, a (111) face can be selectively left by etching in a gas phase using hydrazine (N2H4). Specifically, the (111) face can be left by dry etching using CIF3 and N2H4 as an etching gas.
Further, as a method of applying the energy in the above-mentioned structure, one or plural kinds of methods selected from a heating method, a laser beam irradiation method and an intense light beam irradiation method can be used simultaneously or gradually. For example, a laser beam can be irradiated while heating, a laser beam can be irradiated after heating, heating and the irradiation of a laser beam can be alternately conducted, or heating can be conducted after the irradiation of a laser beam. Also, the laser beam may be replaced by an intense light beam.
In the case where the silicon film is used as a semiconductor film, and an energy is applied to the film to crystallize the silicon film, it is useful to use a metal element that promotes the crystallization of silicon. For example, when an amorphous silicon film formed by the plasma CVD technique or the low pressure thermal CVD technique is to be crystallized by heating, a heat treatment at a temperature of 600xc2x0 C. or higher for 10 hours or longer is required. However, in the case of using a metal element that promotes the crystallization of silicon, the effect equal to or more than that of the above-mentioned heat treatment can be obtained by a heat treatment at 550xc2x0 C. for 4 hours.
Nickel is the hiahest in its effect and useful as the metal element that promotes the crystallization of silicon. Also, one kind of plural kinds of elements selected from Fe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu and Au can be used. In particular, Fe, Pd, Pt, Cu and Au can obtain the better effect next to Ni.
A monocrystal-like region or a substantially monocrystal-like region can be formed in a predetermined region by conducting a crystal growth from the seed crystal. The monocrystal-like region or the substantially monocrystal-like region is defined as a region that satisfies conditions stated below.
No grain boundary substantially exists in the region.
A hydrogen or halogen element that neutralizes a point defect is contained at a density of 0.001 to 1 atm % in the region.
Carbon and nitrogen atoms are contained at a density of 1xc3x971016 to 5xc3x971018 atm cmxe2x88x923 in the region.
Oxygen atoms are contained at a density of 1xc3x971017 to 5xc3x971019 atm cmxe2x88x923 in the region.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor, comprising the steps of:
forming a first silicon film on a substrate having an insulating surface;
bringing said first silicon film in contact with a metal element that promotes the crystallization of silicon and holding said first silicon film:
applying an energy to said first silicon film to crystallize said first silicon film;
patterning said first silicon film to form a region that forms a seed crystal:
etching said seed crystal to selectively leave a predetermined crystal orientation in said seed crystal;
covering said seed crystal to form a second silicon film;
bringing said first silicon film in contact with a metal element that promotes the crystallization of silicon and holding said first silicon film:
applying an energy to said second silicon film to conduct a crystal growth from said seed crystal in said second silicon film.
According to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor, comprising the steps of:
forming a first silicon film on a substrate having an insulating surface;
applying an energy to said first silicon film to crystallize said first silicon film;
patterning said first silicon film to form a region that forms a seed crystal;
etching said seed crystal to selectively leave a predetermined crystal orientation in said seed crystal;
covering said seed crystal to form a second silicon film;
applying an energy to said first silicon film to conduct a crystal growth from said seed crystal in said first silicon film; and
conducting a patterning including at least a removal of the region in which said seed crystal is formed to form an active layer of the semiconductor device.
The above-mentioned structure is characterized in that the region of the active layer thus obtained comprises a monocrystal-like region or a substantially monocrystal-like region. This region is defined as a region in which no grain boundary substantially exists, a hydrogen or halogen element which neutralizes a point detect is contained at a density of 0.001 to 1 atm %, carbon and nitrogen atoms are contained at a density of 1xc3x971016 to 5xc3x971018 atm cmxe2x88x923, and oxygen atoms are contained at a density of 1xc3x971017 to 5xc3x971019 atm cmxe2x88x923.
According to still another aspect of the present invention, there is provided a method of manufacturing a semiconductor, comprising the steps of:
forming a first silicon film on a substrate having an insulating surface;
applying an energy to said first silicon film to crystallize said first silicon film;
patterning said first silicon film to form a region that forms a seed crystal;
etching said seed crystal to selectively leave a predetermined crystal orientation in said seed crystal;
covering said seed crystal to form a second silicon film;
conducting a patterning to form said second silicon film in a rectangular shape;
applying an energy to said second silicon film to conduct a crystal growth from said seed crystal in said second silicon film; and
conducting a patterning including at least a removal of the region in which said seed crystal is formed with respect to said second silicon film to form an active layer of the semiconductor device;
wherein said seed crystal is positioned at a corner of said second silicon film which is formed in the rectangular shape.
A specified example using the above-mentioned structure is shown in FIG. 3. In FIG. 3, a seed crystal 303 is positioned at a corner portion 304 of an amorphous silicon film 302 which is formed in a rectangular shape, and a laser beam which has been processed into a beam linearly is irradiated onto the amorphous silicon film 302 from the corner while being scanned thereon to thereby crystallize the amorphous silicon film 302.
FIG. 3 shows an example in which the silicon film 302 (amorphous silicon film) is patterned in a quadrangle. However, it may be of a square or a rectangle.
According to yet still another aspect of the present invention, there is provided a method of manufacturing a semiconductor, comprising the steps of:
forming a first silicon film on a substrate having an insulating surface;
applying an energy to said first silicon film to crystallize said first silicon film;
patterning said first silicon film to form a region that forms a seed crystal;
etching said seed crystal to selectively leave a predetermined crystal orientation in said seed crystal;
covering said seed crystal to form a second silicon film;
conducting a patterning to form said second silicon film in a polygonal shape;
applying an energy to said second silicon film to conduct a crystal growth from said seed crystal in said second silicon film and
conducting a patterning including at least a removal of the region in which said seed crystal is formed with respect to said second silicon film to form an active layer of the semiconductor device;
wherein said seed crystal is positioned at a corner of said second silicon film which is formed in the polygonal shape.
A specified example using the above-mentioned structure is shown in FIG. 4. In FIG. 4, a seed crystal 404 is positioned at a corner portion 403 of an amorphous silicon film 401 which is patterned in a pentagon of the home base type, and a laser beam which has been processed into a beam linearly is irradiated onto the amorphous silicon film 401 from the corner while being scanned thereon to thereby crystallize the amorphous silicon film 401.
FIG. 4 shows an example in which the silicon film is patterned in a pentagon. However, it may be of a polygon having more corners. It should be noted that as the number of corners is increased, the angle of a corner is necessarily increased more, to thereby reduce such an effect that crystallization progresses from the corner.
According to yet still another aspect of the present invention, a method of manufacturing a semiconductor, comprising the steps of:
forming a first silicon film on a substrate having an insulating surface;
applying an energy to said first silicon film to crystallize said first silicon film;
patterning said first silicon film to form a region that forms a seed crystal;
etching said seed crystal to selectively leave a predetermined crystal face in said seed crystal;
covering said seed crystal to form a second silicon film:
applying an energy to said second silicon film to conduct a crystal growth from said seed crystal in said second silicon film; and
patterning said second silicon film to remove at least a portion where said seed crystal exists;
wherein said second silicon film after having been patterned contains therein a hydrogen of 0.001 to 1 atm % and a metal element that promotes the crystallization of silicon with a density of 1xc3x971016 to 1xc3x971019 atm cmxe2x88x923.
In the above-mentioned structure, a silicon film which is formed typically through the plasma CVD technique or the low pressure thermal CVD technique is used for the first and second silicon films.
The reason why the predetermined crystal surface is selectively left is to conduct the crystal growth so as to produce crystal more approximating monocrystal. Leaving the predetermined crystal surface may be achieved by using etching means having a selectivity with respect to the predetermined crystal surface. For example, using an etchant resulting from mixing H2O of 63.3 wt %, KOH of 23.4 wt % and isopropanol of 13.3 wt % together, a (100) face can be selectively left, as a result of which the seed crystal covered with the (100) face can be selectively left. This is because the etching rate of the above-mentioned etchant with respect to the (100) face is lower than that of other crystal faces.
Also, a (111) face can be selectively left by etching in a gas phase using hydrazine (N2H4). Specifically, the (111) face can be left by dry etching using CIF3 and N2H4 as an etching gas. This is also because the etching rate of hydrazine with respect to the (100) face is lower than that of other crystal faces.
Further, as a method of applying the energy in the above-mentioned structure, one or plural kinds of methods selected from a heating method, a laser beam irradiation method and an intense light beam irradiation method can be used simultaneously or gradually. For example, a laser beam can be irradiated while heating a laser bean can be irradiated after heating, heating and the irradiation of a laser beam can be alternately conducted, or heating can be conducted after the irradiation of a laser beam. Also, the laser beam may be replaced by an intense light beam.
In the case where the silicon film is used as a semiconductor film, and an energy is applied to the film to crystallize the silicon film, it is useful to use a metal element that promotes the crystallization of silicon. For example, when an amorphous silicon film formed by the plasma CVD technique or the low pressure thermal CVD technique is to be crystallized by heating, a heat treatment at a temperature of 600xc2x0 C. or higher for 10 hours or longer is required. However, in the case of using a metal element that promotes the crystallization of silicon. the effect equal to or more than that of the above-mentioned heat treatment can be obtained by a heat treatment at 550xc2x0 C. for 4 hours.
Nickel is the highest in its effect and useful as the metal element that promotes the crystallization of silicon. Also, one or plural kinds of elements selected from Fe, Co, Ru, Rh, Pd, Os, Tr, Pt, Cu and Au can be used. In particular, Fe, Pd, Pt, Cu and Au can obtain the better effect next to Ni.
A monocrystal-like region or a substantially monocrystal-like region can be formed in a predetermined region by conducting a crystal growth from the seed crystal. The monocrystal-like region or the substantially monocrystal-like region is defined as a region that satisfies conditions stated below.
No grain boundary substantially exists in the region.
A hydrogen or halogen element that neutralizes a point defect is contained at a density of 0.001 to 1 atm % in the region.
Carbon and nitrogen atoms are contained at a density of 1xc3x971016 to 5xc3x971018 atm cmxe2x88x923 in the region.
Oxygen atoms are contained at a density of 1xc3x971017 to 5xc3x971019 atm cmxe2x88x923 in the region.
Also, with the removal of the region where a seed crystal exists, the density of the metal element in the monocrystal-like region or the substantially monocrystal-like region can be set to 1xc3x971016 to 1xc3x971019 atm cmxe2x88x923, preferably 1xc3x971016 to 5xc3x971018 atm cmxe2x88x923.
The monocrystal-like region or the substantially monocrystal-like region is selectively formed, and thereafter an amorphous silicon film is formed with covering the seed crystal. Further, an energy is applied to the film by heating or irradiating a laser beam so that a crystal growth can progress from the seed crystal. Then, the monocrystal-like region or the substantially monocrystal-like region can be formed in the periphery of the seed crystal.
The monocrystal-like region or the substantially monocrystal-like region can be formed into a desired region by selecting a region where the seed crystal is formed. Hence, the thin-film semiconductor device formed using that region can be formed into the desired region.
In other words, a device equal to the device using the monocrystal silicon can be formed in a desired region. Also with the use of the operation of a metal element that promotes the crystallization of silicon or the irradiation of a laser beam or an intense light beam a glass substrate weak in heating can be used.
A plurality of semiconductor regions obtained by patterning one monocrystal-like region or substantially monocrystal-like region commonly provide the same crystal axis and rotating angle around the crystal axis, respectively. The xe2x80x9ccrystal axisxe2x80x9d called in this example defines a crystal axis 901 which is directed perpendicularly to a plane 903 in the monocrystal-like region or the substantially monocrystal-like region in FIG. 9.
The orientation of the crystal axis can be made different depending upon a method of forming a starting film directed to the crystal axis and a crystallizing method. Specifically, a value such as a  less than 111 greater than  axial orientation or a  less than 100 greater than  axial orientation can be taken.
The xe2x80x9crotating angle around the crystal axisxe2x80x9d defines an angle indicated by reference numeral 902 in FIG. 9. This angle is of a relative angle which is measured with a reference of an arbitrary orientation.
In the same monocrystal-like region or substantially monocrystal-like region, the crystal axes and the rotating angles therearound are identical or substantially identical to each other.
Here, that the crystal axes are identical or substantially identical to each other is defined as that its deviated angle is in a range of xc2x110xc2x0. Also, that the rotating angles are identical or substantially identical to each other is defined as that its deviated angle is in a range of xc2x110xc2x0.
Therefore, when the same monocrystal-like region or substantially monocrystal-like region is patterned to form a plurality of semiconductor regions, and a plurality of thin-film transistors are formed using those regions, the crystal axes of those active layers ale identical to each other. Similarly, the angles around the crystal axes are identical to each other.
Then utilizing the above fact plural pairs of thin-film transistors using the monocrystal-like region or substantially monocrystal-like region which commonly provide the same crystal axes and angles therearound can be formed as one group. For example, a CMOS Circuit or an invertor circuit which are constituted by the combination of a p-channel type thin-film transistor with an n-channel type thin-film transistor can be comprised of a monocrystal-like region or substantially monocrystal-like region which commonly provide the same crystal axes and anales therearound.